Predicting effect of filler metals on solidification cracking susceptibility of 2024 Al and 6061 Al

ABSTRACT

The susceptibility to solidification cracking was predicted for aluminium welds of 2024 Al made with filler metals 2319, 4043 and 4145 Al and of 6061 Al made with filler metals 4043 (traditional) and 4943 Al (new, higher strength). The maximum |dT/d(f_S)^1/2| (T: temperature; f_S: fraction of solid) was used as the crack susceptibility index. In each case, the index was calculated using the weld metal composition based on the measured dilution level. The predicted crack susceptibility decreased in the order of 2319 Al, 4043 Al and 4145 Al for 2024 Al, and was similar between 4043 Al and 4943 Al for 6061 Al. These predictions agreed well with the experimental results of recent crack susceptibility tests of these welds.     

Effect of modified AA4043 filler on partially melted zone cracking of Al-alloy gas tungsten arc welds

Abstract

The effect of grain refiners (zirconium, Tibor and scandium) added to the fusion zone through AA4043 filler on the partially melted zone (PMZ) cracking in gas tungsten arc (GTA) welded AA6061 alloy was investigated. Welds of AA6061 in thermal tempers of artificially aged condition (T6) were made with continuous current and pulsed current techniques. Varestraint testing was carried out to study PMZ cracking in welds, and optical SEM examination performed to evaluate it. Addition of grain refiners to the fusion zone improved the PMZ cracking resistance very significantly. Pulsed current technique was also found to improve the resistance to PMZ cracking, as a result of the possible reduction in the strain in the PMZ owing to the ductile fine grained fusion zone. Severe PMZ cracking in the welds of AA4043 filler without grain refiners was attributed to a greater amount of silicon rich eutectic at the grain boundaries of the PMZ.     

Hot cracking of welds on heat treatable aluminium alloys

Abstract

The Spot Varestraint test was used to evaluate the hot cracking susceptibility of several aluminium alloys namely 6061-T6, 6061-T6 (H), 7075-T6, 7075-T6 (H). The effects of augment strain, the number of thermal cycles and cold working (rolling) on the cracking susceptibility were investigated, and the total crack length was used to evaluate the hot cracking susceptibility. The results indicate that the number of thermal cycles is irrelevant to the hot cracking susceptibility in the weld fusion zone, but does affect this susceptibility in the heat affected zone (HAZ). More thermal cycles correspond to larger hot cracks in the HAZ, especially in the weld metal HAZ. The hot cracking susceptibility of materials increased with augment strain in both the fusion zone and the HAZ. Cold working of the materials can reduce their hot cracking susceptibility. The hot cracking susceptibility of 7075-T6 aluminium alloys is higher than that of 6061-T6. There was significant Cu segregation in the HAZ of 7075-T6 aluminium alloy, resulting in a higher susceptibility to hot cracking in this zone.     

Cracking behavior in a dissimilar weld between high silicon nodular cast iron and ferritic stainless steel

In this work, the microstructural evolution and cracking behavior of a dissimilar weld between high silicon nodular cast iron and ferritic stainless steel was investigated. An austenitic filler metal (Y309) was employed to produce the dissimilar weld. Microstructural analysis revealed that cracking formed at the unmixed zone (UMZ) and propagated into the partially melted zone (PMZ) in the bond line between the cast iron and the Y309, with hard layers formed around the bond line. The cracking behavior was strongly related to the difference in the melting points of cast iron and the Y309 filler metal, the local liquation of the laves phase, and the constitutional liquation between the graphite and austenite phases in the PMZ.     

Effects of grain size and precipitation on liquation cracking of AZ61 magnesium alloy laser welding joints

Abstract

Four kinds of wrought AZ61 alloy sheets with different microstructural features were successfully welded by CO₂ laser beam butt welding. Welding joints without visible pores were obtained under optimum process parameters. Effects of grain size and precipitation on liquation cracking behaviours of the laser welding joints were investigated. As far as the as rolled alloy sheets were concerned, liquation in the partially melted zone (PMZ) was visible along grain boundaries, and the extent of liquation was more serious in the alloy sheets with larger grains. As far as the as aged alloy sheets were concerned, plenty of precipitates (β-Mg₁₇Al₁₂) were involved and liquation in the PMZ was found both at grain boundaries and within grains. Moreover, the extent of liquation was more serious in the alloy sheets with more precipitates. It is promising to reduce liquation cracks in the PMZ of magnesium alloys by grain refinement, reducing the size and the quantity of the low melting point phase, and modifying its distribution.     

ZK60镁合金激光焊接接头的液化开裂(英文)

采用激光对ZK60镁合金板材进行焊接,研究焊接接头半熔化区的显微组织。结果表明:铸态合金半熔化区中沿晶分布的共析混合物在焊接过程中出现液化,其凝固组织呈现亚共晶结构,这种结构导致晶界处的Zn元素偏析更为严重,从而加剧了该区域的开裂倾向;半熔化区液化开裂的主要原因是凝固最终阶段液相不足使得半熔化区液化部位产生缩孔,并成为裂纹源,在凝固收缩及热收缩所产生的拉应力作用下,裂纹沿弱化的晶界扩展;降低焊接热输入和对母材进行轧制等塑性加工均有利于提高该合金焊接时的抗液化裂纹性能,后者的作用主要在于细化共晶相的尺寸并改变其分布。     

Research on Prediction Method of Liquation Cracking Susceptibility to Magnesium Alloy WeldsEI北大核心CSCD

Magnesium alloys has a wide application prospect due to their good properties, such as high specific strength and specific stiffness, but the susceptibility of liquation cracking is also pretty high. The liquation in partially melted zone of AZ-series magnesium alloys were investigated with circular-patch welding test. The AZ91, AZ31 base alloys were welded with AZ61 and AZ92 filler wires by using the cold metal transter metal inert-gas (CMT-MIG) welding. The results show that, the liquation occurred along the weld edge of AZ91 with the eutectic reaction occurring between gamma(Mg17Al12) phase and Mg-rich phase. The liquation susceptibility of AZ31 was pretty low as gamma(Mg17Al12) was not present in base metal of AZ31. Meanwhile, a new method for predicting liquation cracking based on binary phase diagram was proposed. When the initial solidification temperature of weld is higher and the solidification temperature range of weld is shorter than those of base metal, the liquation crack susceptibility of weld is mostly higher. When the initial solidification temperature of weld is close to or below that of base metal, and the solidification temperature range of weld is close to or longer than that of base metal, the liquation cracking susceptibility of weld is lower. This method worked well on predicting the effect of composition of base metal and filler wires on liquation cracking, and the predicting results are consistent with the experimental results. That is, the liquation cracking susceptibility is higher with AZ91 base metal used than that with AZ31 base metal. And, the liquation cracking susceptibility is lower with AZ92 filler wire than that with AZ61 filler wire.     

Grain Refinement in Al-Mg-Si Alloy TIG Welds Using Transverse Mechanical Arc Oscillation

Reduction in grain size in weld fusion zones (FZs) presents the advantages of increased resistance to solidification cracking and improvement in mechanical properties. Transverse mechanical arc oscillation was employed to obtain grain refinement in the weldment during tungsten inert gas welding of Al-Mg-Si alloy. Electron backscattered diffraction analysis was carried out on AA6061-AA4043 filler metal tungsten inert gas welds. Grain size, texture evolution, misorientation distribution, and aspect ratio of weld metal, PMZ, and BM have been observed at fixed arc oscillation amplitude and at three different frequencies levels. Arc oscillation showed grain size reduction and texture formation. Fine-grained arc oscillated welds exhibited better yield and ultimate tensile strengths and significant improvement in percent elongation. The obtained results were attributed to reduction in equivalent circular diameter of grains and increase in number of subgrain network structure of low angle grain boundaries.     

Weld cracking and joint strength of 2219 by MIG welding

Weldability of Al–Cu series alloy 2219 with MIG process was investigated in comparison with that of Al–Cu-Mg series alloy 2024. On weld cracking sensitivity, 2219 is superior to 2024 and as for the combination with filler metal, the decrease in Mg content in weld metal causes crack resistance to increase. And a liquation cracking in heat-affected zone was easily initiated in the case of Mg contents more than 1.6 mass% and Cu/Mg (ratio in mass%) less than 1.8 in weld metal. Welded joints were mostly fractured in weld metal even with reinforcement during tensile testing, so the intensification of weld metal is directly connected to the improvement in joint strength and fractured mode. The results of the investigation of correlation between the strength and chemical composition in weld metal revealed that the joint strength increased with an increase in magnesium and manganese but encouraged the weld cracking simultaneously. However, the author has also found that silicon was available for decreasing weld crack and the possibility of consistency with joint strength and crack resistance by control of these contents of Mg, Mn, and Si.     

Multicycle fatigue strength of welded joints of steel S500MC

Microcracking susceptibility in the dissimilar multipass weld metal of alloy 690 and low-alloy steel A533B was evaluated, and the effect of dilution on hot cracking (ductility-dip and liquation cracking) behaviour was investigated. In order to simulate the dissimilar multipass weld metal of alloy 690 to A533B steel, the A533B plate was welded under various dilution ratios using alloy 690 filler metal with different contents of P and S. Several weld metals, which had different alloy compositions at the fixed (P+S) content, were manufactured, and then ductility-dip and liquation cracking susceptibilities of the reheated weld metals were evaluated by the spot-Varestraint test. Ductility-dip cracking susceptibility heightened as the dilution ratio was increased even when the amounts of P and S were fixed. The increased dilution ratio (contamination of Fe into the weld metal) should reduce the tortuous character of the grain boundary (GB) due to inhibiting the constitutional supercooling (the instability of the solidification boundary), as well as enhance the GB embrittlement due to promoting the GB segregation of P and S. Furthermore, the liquation cracking susceptibility slightly heightened with an increase in the dilution ratio at the fixed (P+S) content. The increased liquation cracking susceptibility would be attributed to the enhancement of solidification segregation of P and S with increasing the dilution ratio.     

The effect of annealing twin-generated special grain boundaries on HAZ liquation cracking of nickel-base superalloys

The susceptibility to weld heat-affected-zone (HAZ) liquation cracking of wrought Waspaloy and Alloy 718 was quantified by using hot ductility testing. The intergranular (IG) cracking behavior of these alloys was influenced by long term isothermal heat treatments. Such long holds at the solution temperature resulted in continuous grain growth in Waspaloy. However, the IG liquation cracking was not solely controlled by grain size. Annealing twin-generated special grain boundaries increased in volume fraction as grain size increased and reduced the tendency for IG cracking. Intense δ phase precipitation occurred in Alloy 718 following the long isothermal holds. δ phase pinning of grain boundaries restricted grain growth and hence the fractional increase of special grain boundaries. However, special grain boundaries did provide resistance to IG liquation cracking once the δ-phase was dissolved using a “rejuvenation” heat treatment.     

Microcracking in multipass weld metal of alloy 690 Part 3 – Prevention of microcracking in reheated weld metal by addition of La to filler metal

Abstract

The effect of addition of La to a filler metal on microcracking (ductility dip cracking) in the multipass weld metal of alloy 690 was investigated with the aim of improving its microcracking susceptibility. The susceptibility to ductility dip cracking in the reheated weld metal could be greatly improved by adding 0·01–0·02 wt-%La to the weld metal. Conversely, excessive La addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0·01–0·02 wt-%La to the weld metal, implying that the ductility dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of La. The liquation and solidification cracking resulting from excessive addition of La to the weld metal is attributed to the formation of liquefiable Ni–La intermetallic compound. A multipass welding test confirmed that microcracks in the multipass weldment were completely prevented by using a filler metal containing an addition of 0·01 wt-%La.     

Anion effects on the stress corrosion cracking behaviour of aluminium alloys

The stress corrosion cracking behaviour of plate material of the aluminium alloys 2024‐T351, 8090‐T8171, 7475‐T651, and 7075‐T7351 was investigated performing constant load tests. Short transverse tensile specimens were permanently immersed in aerated aqueous 0.6 M Na₂Cl solutions with additions of Na₂SO₄, NaNO₃, NaHCO₃, NH₄HCO₃, Na₂HPO₄, Na₂SO₃ or Na₂CO₃. The concentration of the added salts was 0.06 M. The applied stress was 100 MPa, except with 7075‐T7351 specimens, which were loaded at 300 MPa. Environment induced failure was not observed in neutral 0.6 M NaCl solution. The various salts added promoted intergranular stress corrosion cracking with the alloys 2024‐T351, 8090‐T8171, and 7475‐T651. Threshold stresses were generally below 100 MPa. For 8090‐T8171 exposed to chloride containing electrolytes with additions of sulfate, hydrogen phosphate, or sulfite, threshold stresses were approximately 100 MPa or higher. Similar results were obtained for 7475‐T651 plate when immersed in chloride‐hydrogen phosphate and chloride‐carbonate solutions. Alloy 7075‐T7351 was resistant against intergranular stress corrosion cracking. Specimens suffered pitting corrosion during immersion in the corrosive environments. Failure observed with 7075‐T7351, in particular when exposed to the chloride‐nitrate solution, was associated with reduction of cross‐sectional area due to pitting and transgranular stress corrosion cracking.     

Controlling weld metal dilution for optimised weld performance in aluminium

Abstract

It is demonstrated how the current trend towards high speed, narrow groove welding, and the corresponding shift towards high base metal dilution, may result in decreased weldability for 6xxx and 7xxx aluminium alloys. In particular, variations in base metal dilution for extrusion alloys 6082 and 7108 have been examined for welds made with 5183, 5356, 5654, and 4043 filler alloys, particularly at high dilution ratios. The less common filler alloys 5039 and Safra 66 are also considered. Dilution curves superimposed upon existing hot cracking curves show that cracking susceptibility increases rapidly with base metal dilution for these alloys. Establishing an upper limit for dilution to avoid hot cracking, for a specific engineering application, also requires a knowledge of restraining conditions. For conditions of high restraint, i.e. rigid fixturing, enforcing an upper limit for base metal dilution will become critical. The effect of dilution on weld strength is also considered.     

Oxide formation on aluminium alloys in boiling deionised water and NaCl, CeCl3 and CrCl3 solutions

Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy have been employed to provide depth, surface chemical and morphological information respectively for a range of Al-alloys treated for 2 h at 90-100 °C in either deionised water (DIW), 30 mM NaCl, 10 mM CeCl₃ or 10 mM CrCl₃ solutions. Alloys included Al sheet 1100-O, 2024-T3, 3004-H19, 5005-O, 6061-T6 and 7075-T6. In DIW all alloys developed the same oxide thickness with a boehmite-like appearance. In NaCl and CeCl₃ solutions the oxide thickness varied with alloy composition but was considerably thicker than the deionised case and maintained a boehmite-like appearance. Ce was distributed throughout the oxide but at low levels. In all cases some Ce^IV was detected on the surface of the oxide, the remainder being Ce^III. In CrCl₃ solution, the oxide thickness was extremely thin with the appearance of a dense oxide rather than a boehmite-type structure.     

铁道车辆用铝材的焊接特性

对高速列车用６０６３、６０６１、９１９（相当于７００５）铝合金母材及与之相匹配的焊丝（４０４３、５１８３、５３５６铝合金丝）施以ＭＩＧ焊接之后的焊区强度、硬度以及焊接接头的腐蚀倾向、残余应力水平和常见的焊接裂纹与气孔等缺陷进行了分析和研究。结果表明，由于产生了软化，焊缝及热影响区的强度和硬度均低于母材；从综合效果来看，以母材６０６１合金匹配４０４３焊丝为佳；从焊后强度和刚度看，中空型材的截面以斜筋截面为优；从焊接接头的可靠性看，以纵向ＭＩＧ自动焊接对接为最好     

Effect of aging time and temperature on exfoliation corrosion of aluminum alloys 2024‐T3 and 7075‐T6

Two types of aluminum alloys, 2024‐T3 and 7075‐T6, have been selected in this study to investigate the effect of metallurgical aspects on exfoliation corrosion. To determine and evaluate the metallurgical effects of heat treatments on corrosion behaviour of these alloys, G34 ASTM test was selected to investigate the exfoliation corrosion behaviour. The results showed that with increasing the aging time for the aluminum alloy type 2024‐T3 the susceptibility to exfoliation corrosion increases, while for type 7075‐T6 decreased. These results refer to precipitation of the intermetallic compound phases such as CuAl₂, and MgZn₂, in 2024‐T3 and 7075‐T6 respectively. The amount of these phases increases with increasing the aging time for both alloys. The investigations showed the phases that initiate in 2024‐T3 act as anode sites while in 7075‐T6 they act as cathode sites.     

Characterisation of solidification cracking in pulsed Nd:YAG laser welding of 2024 aluminium alloy

Abstract

Aluminium alloy AA2024 is one of the most susceptible alloys to solidification cracking. The influence of Nd:YAG laser welding parameters on cracking severity of AA 2024 alloy was studied. Welding was performed in two modes: single spot welding and overlap spot welding. In single spot welding mode, the formation of columnar zone increases cracking severity in the fusion zone. In overlap spot welding mode, the solidification cracks were characterised as: cracks propagated from previous spot, cracks initiated from the fusion line with the previous spot, and cracks initiated from the fusion line with the base metal. It was established that in comparison there is very limited tendency for initiation of new cracks from the fusion line with the weld metal of a previous spot.     

On the Stress corrosion cracking behaviour of aluminium alloy sheet in an aqueous solution of 3% NaCl + 0.3% H2O2

The stress corrosion cracking (SCC) behaviour of aluminium alloy sheet was investigated in the long transverse direction using the slow strain rate testing technique. The synthetic environment used was an aqueous solution of 3% NaCl + 0.3% H₂O₂. No indications of SCC sensitivity are observed for the alloys 2024-T351, 8090-T81, and 2091 CPHK-T8X. The alloys 2091 T8X and 6061-T4 are found to be susceptible to intergranular stress corrosion cracking. At strain rates below 4 · 10^?7 s^?1, the slow strain rate testing technique indicates a slight SCC sensitivity with alloy 6013-T6. Fractography reveals transgranular stress corrosion cracking. Transgranular stress corrosion cracking is also observed with 6061-T4 specimens which are dynamically strained at strain rates below 5 · 10^?7 s^?1. Aqueous 3% NaCl solution with hydrogen peroxide addition promotes pitting and intergranular corrosion. The loss of ductility caused by these corrosion processes interferes with the evaluation of the results of the slow strain rate testing technique.     

Galvanic corrosion of A1 alloys — II. Effect of solution composition

Galvanic corrosion of the A1 alloys 1100, 2024, 2219, 6061 and 7075 coupled to Cu, stainless steel 304L, Ti-6A1-4V, 4130 steel or zinc has been studied in 3·5% MaCl, tapwater and distilled water using electrochemical and weight loss data. In 3·5% NaCl the galvanic effect decreases in the order Cu > 4130 steel > SS304L > Ti-6A1-4V for A1 alloys coupled to one of these metals, while in tapwater and distilled water the ranking is Cu > SS304L ～ Ti-6A1-4V > 4130 steel. Zinc, although being the anode in all galvanic couples, can sometimes accelerate corrosion rates of A1 alloys. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3·5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing galvanic corrosion behaviour of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of A1 6061 is, for example, higher in tapwater with Cu as cathode than in 3·5% NaCl with SS304L or Ti-6A1-4V as cathode.